The use of restorative composites in dentistry has been primarily driven by the esthetic features of these materials. Interest in dental composites as an alternative to amalgam has been further promoted by the public's concern about mercury release from dental amalgam. Despite their extensive use, the short clinical lifetime of composites is a significant limitation. While the clinical lifetime of traditional mercury-containing dental amalgam restorations is generally 10-20 years, the lifetime for methacrylate-based composite restorations is about 8 years in anterior sites and as little as 2-4 years in posterior sites.
The primary factor in the premature failure of composite restorations is recurrent caries at the margins of these restorations. Recurrent decay is most often localized gingivally and is linked to the lack of a consistent seal at the tooth/material interface. Water in the mouth is a major interfering factor when bonding adhesives and/or composites to the tooth. The water content of the dentin surface varies as a function of depth, the nature of the substrate (i.e. caries-affected or healthy dentin) and the presence of residual rinse water.
Effective bonding at the prepared tooth/composite material interface requires dentin adhesives that provide superior properties and rapid polymerization under clinical conditions. The reactivity and the mechanical behavior are influenced by the photoinitiator system and curing conditions.